1. Field of the Invention
The present invention relates to a or structure (coupling) for connecting tubes such as plastic tubes to each other, particularly to a connecting structure excellent in sealing performance suitably used in a piping system for medicine or ultra-pure water.
2. Description of the Related Art
Tube connecting structures for connecting plastic tubes used in a piping system for medicine or ultra-pure water have been known, as shown in FIGS. 11 to 13.
In a structure shown in FIG. 11, presser members 303, 304, also referred to as ferrules are welded, respectively, to ends of opposed two tube members 301, 302 to be connected to each other. A gasket member 305 is disposed between the presser members 303, 304 and compressed together with the presser members 303, 304 by a clamp member 306. In another structure shown in FIG. 12, presser members 313, 314 are screw-engaged with the outer circumference of opposed two tube members 311, 312 to be connected to each other. A gasket member 315 is disposed between the presser members 313, 314 and compressed together with the presser members 313, 314 by a clamp member 316. In a further structure shown in FIG. 13, when opposed two tube members 321, 322 are molded, presser members 323, 324 are attached, respectively, to ends of the tube members 321, 322 to be connected to each other by an insert molding. A gasket member 325 is disposed between the presser members 323, 324 and compressed together with the presser members 323, 324 by a clamp member 326.
According to the above-mentioned prior art connecting structures, an adaptation for attaching or fixing the presser members to the tube members is troublesome and requires skill to obtain a desired accuracy. If the desired accuracy is not obtained, the sealing performance is insufficient, which is a fatal defect in a connecting structure used in a piping system for dealing with medicine or ultra-pure water.
Also, in the above-mentioned prior art structure, it is necessary to prepare tube members having special connecting ends as described in accordance with positions to be connected together when the piping system is installed. Further, if it is necessary to change the piping after the installation, a quick response thereto is impossible.
The present invention has been made in view of the above problems in the prior art, and provides a novel tube connecting structure simple in structure, easily adaptable to various tubes, and capable of obtaining a high sealing performance in a stable manner. This tube connecting structure could also quickly respond to a requirement for a variation in piping system even after the installation thereof.
According to the invention defined by claim 1, a tube connecting structure, for connecting two tubes with each other, is provided and comprises a gasket member having a central opening and first and second annular recesses formed on opposite sides thereof along the outer periphery of the central opening, first and second tube members, each having a folded edge portion formed by folding an end thereof over the outer circumference of the tube member, wherein a convex end of the folded edge portion is brought into tight contact with the annular recess of the gasket member, first and second outer rings, each mounted onto the outer circumference of a body portion of the tube member so that a front end thereof is located behind the convex end of the folded edge portion and a rear end thereof is out of the folded edge portion, first and second presser members, each mounted onto the outer circumference of the tube member and having a contact section with the gasket member and an outer ring pressing section for pushing the rear end of the outer ring toward the mating outer ring, and a clamp member for compressing the first and second presser members together against the gasket member.
According to the invention defined by claim 2, a tube connecting structure for connecting two tubes with each other is provided, comprising a gasket member having a central opening and first and second annular recesses formed on opposite sides thereof along the outer periphery of the central opening, first and second tube members, each having a folded edge portion formed by folding an end thereof over the outer circumference of the tube member, wherein a convex end of the folded edge portion is brought into tight contact with the annular recess of the gasket member, first and second outer rings, each mounted onto the outer circumference of a body portion of the tube member so that a front end thereof is located behind the convex end of the folded edge portion and a rear end thereof is out of the folded edge portion, a male screw member mounted onto the outer circumference of the first tube member and having an outer thread, a contact section with the gasket member and an outer ring pressing section for pushing the rear end of the first outer ring toward the second outer ring, and a female screw member mounted onto the outer circumference of the second tube member and having an inner thread to be engaged with the outer thread of the male screw member and an outer ring pressing section for pushing the rear end of the second outer ring toward the first outer ring.
According to the invention defined by claim 3, a connecting structure for connecting a flanged connecting member having a flange surface to a mating tube member is provided, comprising a gasket member having a central opening in correspondence to an opening of the flanged connecting member, a contact surface in tight contact with the flange surface of the flanged connecting member on one side and an annular recess formed along the periphery of the central opening on the other side, a mating connecting tube member having a folded edge portion formed by folding an end thereof over the outer circumference thereof so that a convex end of the folded edge portion is brought into tight contact with the annular recess of the gasket member, an outer ring mounted onto the outer circumference of a body portion of the tube member so that a front end thereof is located behind the convex end of the folded edge portion and a rear end thereof is out of the folded edge portion, a presser member mounted onto the outer circumference of the tube member and having a contact section with the gasket member and an outer ring pressing section for pushing the rear end of the outer ring in the axial direction of the tube member, and a clamp member for compressing the presser member together against the gasket member.
According to the invention defined by claim 4, a tube connecting structure as defined by any one of claims 1 to 3 is provided, wherein the tube member is an elbow, a tee, a cross or a reducer.